Rear wheel nut
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raleighnut
Legendary Member
- Location
- One of the 'Elite'
M9 is front M10 rear on classic bikes.
Out of interest, what is the reason for this difference?
raleighnut
Legendary Member
- Location
- One of the 'Elite'
The axle is thinner on a front wheel so an M10 would fall off.
overmind
My other bike is a Pinarello
- Location
- Reading, Berkshire
I think the reason for the different thicknesses of axle might be that the front wheel (hub) is not as wide (and possibly does not carry as much load) as the rear wheel. Therefore, it can have a thinner axle.
I googled this theory but could not find anything.
Last edited:
Ajax Bay
Guru
- Location
- East Devon
QR and bolted axles have been 9mm/100mm front/rear for aeons, presumably for exactly the engineering design reason @overmind rehearses. As well as shear forces, a rear axle has to resist more bending force than a front one because the bearings are further away from the dropouts, as well as the rear taking a heavier load (in normal riding).
This Jan 2017 article (extract) hoped that, for thru-axles, 12mm would become the 'norm' front and rear:
"the bike industry is settling on a standard, with most manufacturers following Shimano’s lead — 12x100mm front thru-axles are becoming the norm and most rear ends now use 12x142mm axles. This allows an 11-speed cassette and the brake rotor to fit without too asymmetric a rear wheel built on a narrow spoke placement."
This Jan 2017 article (extract) hoped that, for thru-axles, 12mm would become the 'norm' front and rear:
"the bike industry is settling on a standard, with most manufacturers following Shimano’s lead — 12x100mm front thru-axles are becoming the norm and most rear ends now use 12x142mm axles. This allows an 11-speed cassette and the brake rotor to fit without too asymmetric a rear wheel built on a narrow spoke placement."
Ian H
Ancient randonneur
What you really need to secure your rear wheel is pukka wheel-nuts with free-spinning captive washers. You may well find them in Halfords (which is where I found the last pair I bought).
https://www.sjscycles.co.uk/hub-spares/10mm-track-nuts/
https://www.sjscycles.co.uk/hub-spares/10mm-track-nuts/
midlife
Guru
rogerzilla
Legendary Member
Cheap rear axles can be 3/8". Campagnolo use a unique 10mm x 26tpi, just so you have to pay £21 each for a track nut 
That free-spinning, is that to minimalize frame dropout damage?
raleighnut
Legendary Member
- Location
- One of the 'Elite'
Nah the washer part is serrated/toothed, what it does do is give a better 'tightness' and grip to the nut so less likelihood of the axle slipping in the dropouts.
A serrated/toothed washer fixed on a nut will damage the dropout when the nut is turned.
If free spinning (relative to the nut so not fixed) then the nut / washer contact can slip so the washer doesn't turn, or turns less, with the nut, preventing dropout damage while still prevent axle slipping in the dropout.
My previous fixed gears started to show serious dropout damage due to chain retensioning. I solved it by replacing the serrated washer+nut fixed combo by tandems common nut + spring washer, sometimes with a flat washer inbetween, depending on the available length of the axle.
A single piece but freespinning, appears to me as a better choice since it's one part.
Yellow Saddle
Guru
- Location
- Loch side.
Strength, as mentioned above.
The front could be 10mm (I dunno why it isn't) but the back cannot be 9mm.
The highest forces in a bike frame are at the right chainstay/chain and rear axle.
Under tension, the rear axle bends in a bow as the chain pulls forward on the sprocket.
The narrower the distance between the two drop-outs (called the OLD for over locknut dimension), the smaller the bow and conversely, the opposite.
Another factor that affects the bow is the location of the right side wheel bearing. If it is close to the locknut, it supports the axle better than when it is moved further inboard. This became very obvious with the advent of 8-speed freewheels (not freehubs). This was just one step up from 7-speed but the OLD changed from 126mm to 130mm and the right bearing was now just too far inboard for what a threaded, 10mm hollow steel axle could withstand and we had plenty of "bent" axles as a result. I put bent in quotations because these axles weren't bent, they were cracked. The cracks weren't easy to see but could be shown by removing the axle, blocking one end of the axle/tube, immersing it in water and blow on the other end. Bubbles would emerge just there were the outboard bearing sat on the axle.
The remedy for this was the freehub, which had a different design and bearings further outboard. It solved the problem even though it retained the wide OLD of 130mm (or more on MTBs) and 8-speed cassette spacing.
That explains why some nuts I received didn't screw on my rear axle.
My previous fixed gears tensioned the chain along sliding the rear wheel further backwards in the dropouts.
The problem was that over time the dropouts got damaged by the many nut tensionings, especially by the grip-giving builtin washer profile some nuts had. Also, the thread inside the nuts wore. So I asked for some spare nuts for the rear, and apparently I was given some 9 mm too, inflicting me a nasty surprise along the road, when I discovered my wheel was loosening due to worn thread and my spare didn't fit.
They had better chosen 10 mm for the front too, instead of that different and also uncommon 9 mm size.
The only reason I can think of is to save some weight. A tiny difference, not worth the mess of two nut sizes, imho.
My previous fixed gears tensioned the chain along sliding the rear wheel further backwards in the dropouts.
The problem was that over time the dropouts got damaged by the many nut tensionings, especially by the grip-giving builtin washer profile some nuts had. Also, the thread inside the nuts wore. So I asked for some spare nuts for the rear, and apparently I was given some 9 mm too, inflicting me a nasty surprise along the road, when I discovered my wheel was loosening due to worn thread and my spare didn't fit.
They had better chosen 10 mm for the front too, instead of that different and also uncommon 9 mm size.
The only reason I can think of is to save some weight. A tiny difference, not worth the mess of two nut sizes, imho.
